1. Field of the Invention
The present invention relates to a method of making absorbable surgical threads and can be used in medicine biology and veterinary science.
At present absorbable threads are widely used in medical practice. They do not require such a manipulation as thread removal and provide for a proper cosmeticability of the cicatrices resulting from surgical operations.
In order to be successfully used, the absorbable threads should possess a sufficient strength. However, conventional absorbable threads are of inadequate mechanical strength. Therefore efforts are constantly undertaken to develop novel methods of making absorbable threads based on cellulose which are characterized by a higher mechanical strength.
2. Description of the Prior Art
There is known in the art a method of making surgical threads (U.S. Pat. No. 2,537,979) which consists in oxidizing cellulose with nitrogen dioxide. However, as distinct from the method described above, the oxidation here is carried out till the content of carboxyls is 4 to 12.5%. The time of making said surgical sutures is 64 hours. The process is carried out at a temperature of 25.degree. C. Having been treated with nitrogen dioxide, the threads are washed with distilled water and dried. The ratio between the value of the tensile strength of the absorbable threads produced due to the treatment of the initial threads and the value of the tensile strength of the initial threads prior to the treatment is 36.8 to 43.5%.
As a result of the oxidation of the cellulose threads with nitrogen oxides there occurred a destruction of the supermolecular structure of the cellulose threads because of inculation of large molecules of N.sub.2 O.sub.4, rupture of intermolecular hydrogen bonds cellulose-cellulose and cellulose-water-cellulose, substitution of a part of C.sup.6 H.sub.2 OH-groups by larger C.sup.6 OOH-groups. Therefore, the surgical absorbable threads produced by said method are of a low mechanical strength and of a high swelling property in biological media.
As noted in the above Patent, such a thread completely lost its strength within 5 days. The testing was carried out in a phosphate buffered solution having a pH of 7.5 at a temperature of 37.degree. C. where a thread is absorbed slower than in living tissues. No testing of the thread placed in living tissues was carried out.
Thus, the above-described method does not provide for the manufacture of absorbable surgical threads having a high mechanical strength and a low swelling property in beological media.